The present invention is related to a method of testing defects in material, particularly, semiconductor material.
Semiconductor is widely used in modern electronic devices such as transistors, silicon control rectifiers, integrated circuits, solar cells etc. In large area devices, the quality of the semiconductor material is very important for the yield in production. Any defects in the material whether originally grown in the crystal or induced during processing can cause the device to malfunction. It is important to inspect the material before costly processing the device. Also if any defect is introduced during processing, the particular semiconductor wafer should be discarded from further processing.
Visual inspection of the semiconductor wafer is often inadequate, because defects may be hidden beneath the surface. Besides, visual defect may not be correlated the semiconductor electrical properties such as lifetime, diffusion lengths, etc. which are important to device characteristics.
Photo response using a scanning light has been used to inspect the semiconductor wafers. Photo response results from photovoltaic effect. However, photo response can only be effected with a p-n junction or a Schottky barrier. Unfortunately, after the p-n junction is formed, the junction becomes a permanent part of the structure and cannot be removed.
If Schottky barriers are used, a metal must be deposited on the wafer, which must be removed subsequently. Besides, a metal generally has poor optical transmission, which reduces the sensitivity of the measurement. Thus, the extra processing steps and the poor optical transmission make this scheme unattractive.
What is needed is a method of inspecting a semiconductor wafer which is nondestructive and does not add any processing steps.